A light blue ensign with the national flag in the canton and the roundel in the lower fly. I assumed that the flag would follow the other ensigns regarding the ratio.
Source: The World of FlagsŽeljko Heimer, 14 February 2001

A note in Album des Pavillons indicates that the national flag is painted on the fin. The marking
is a roundel consisting of two concentric disks, the outer green and the inner
red, the inner having diameter of half the outer one.Željko Heimer, 15 February 2001

Fin Flash

The fin flash is basically the national flag. The image at
Cochrane & Elliott (1998)
show the red ball centered on the green.Dov Gutterman, 11 June 2004